Preservative and contact coating for light sensitive devices



E. D. WILSON 2,172,232

PRESERVATIVE AND CONTACT COATING FOR LIGHT SENSITIVE DEVICES Sept. 5, 1939.

Filed March 5, 1936 Nafura] penn /6 filma/af Fmg Aa of' Ag Barrier Plane CU2 O INVENTo E'd/Z E Wj/Sorz- ATTOR EY Patented sept. 5, 1939o UNITED STAT-Es PREsERvATlvE Foa LIGHT Earl D. Wilson,

AND CONTACT COATING SENSITIVE DEVICES Wilkinsburg, Pa.,

assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa.,

Pennsylvania a corporation of Application March 5, 1936, Serial No. 67,277

9 Claims.

to preservative coatings preservative coatings for light- My invention relates and especially to sensitive devices.

It is an robject of my invention to provide a preservative coatin-g for light-sensitive devices and in particular for light-sensitive devices of the copper oxide type.

Another object of my invention is to provide a coating for a light-sensitive device of the copper oxide type which has a conductive portion therein for the purpose of making an electrical contact with the device.

As stated above, the invention has particular application to the copper-oxide type of cell and especially to the particular type of copper oxide s cell which I designate as having a front-wall effect, namely, one in which the light causes an emission from the copper oxide to a translucent or transparent conductive material superimposed thereon. lIn operation I have found that the translucent material being very thin is apt to be damaged by handling or by improper contact with other objects.

Furthermore, the conductive metal which is preferably of the noble metals, silver, gold or platinum, is acted upon chemically if exposed for a long time to the atmosphere. The result is that the cells rather rapidly lose their sensitivity. Accordingly, I have devised a coating for these light-sensitive cells that will protect the noble metal conductive film from chemical action, from mechanical contact and which will preserve the sensitivity of the ycell to light. I also have devised how to make electrical contact at certain portions through the protective layer to the noble metal without exposing the noble metal film to the atmosphere or to the direct pressure of a metal connector.

Other objects of my invention will'become apparent upon reading the following description and drawing wherein the single figure is a cross section through a light-sensitive cell having my preferred form of preservative and contact coating thereon.

As previously explained, my invention is particularly adapted for the copper oxide type of light-sensitive device. 'I'he copper oxide lightsensitive device is, of course, formed preferably from a copper disk l by oxidizing one surface thereon as a layer of copper oxide in the cuprous form. Instead of utilizing the type of cell in which the action takes place between the copper oxide and the copper, I prefer to use what I designate as the front-wall or obverse type of copper oxide cell. This particular type of ccll is specfically described in my Patents 2,095,781, 2,095,782 and 2,095,783 granted Oct. 12, 1937. The copper oxide Il is formed on the copper disk" at such a depth that the copper oxide is substantially opaque in order to prevent any response to light at the servative film that makes juncture between the copper oxide and copper. It is also possible that the temperature at which the copper oxide is formed on the copper helps in destroying the response in respect to light between the copper oxide and the copper. As explained -in the applications previously referred to, I bombard the surface of the copper oxide to produce a barrier plane l2 of a polarized gas thereon and then evaporate a translucent lm of noble metal I3, namely, silver, or gold or platinum thereon. This translucent film may, of course, be thin enough to be also transparent. I have found that in operating the device the cell rather rapidly loses a large portion of its initial sensitivity and the noble metal is apt to be damaged by handling or by exposure to the atmosphere with a consequent chemical action.

Furthermore, electrical metal contact members on the noble metal film would wear through the noble metal and make contact with the copper oxide. Accordingly, I have devised a precontact to the translucent metal without chemical or mechanical contact damage thereto.

For this protective film, I prefer to use a resin coating and preferably the class of resins known as natural resins or gums. Preferred specific materials in this class of naturalI resins are rosin collophony, abietic acid, ester gum or glycerized rosin. By use of this protective coating, I prevent the deterioration of the cell.

I found, however, that it was advisable to improve the coating so that it `would be more flexible and tougher at lower temperature and that it would stand a low temperature Without cracking. Accordingly, I prefer to use one orv more of the Well known group of plasticizers in the natural resin coating. These plasticizers are preferably of the waxes or glycerin type and may be preferably of beeswax although paraffin, Japan wax, normal butyl phthalate, ethylene or other glyco'ls are readily available. The proportion of the plasticizer depends upon the temperature range to which the device may be subjected. The plasticizer can extend from 2% to 25% of the natural resin coating, but this range can be limited to 5% to 15% for Northern United States and I have found that 121/2% of plasticizer works excellently.

Some of the cells I noticed have lost as much as 251% of their original sensitivity in a day but the application of this preservative coating successfully prevented this former rapid deterioral tion of sensitivity. Y

Electrical contact to the noble metal film had been made by use of copper fingers bearing upon the edge of the noble metal film. These copper such as silver or zinc and granulate it. The

. book of Chemistry and Physics, published by metal may be of any desired shape vof powder such as ne granules or even fiaked. I prefer, however, to sift the metal through a mesh of from'50 to 200 fineness. The powdered metal can be sifted upon the surface of the natural resin and preferably restricted to the portion represented by the rim or circumference region I5.v This powdered metal will sink through the fluid resin upon application of heat to about 100 C. and make contact-with the gold or silver film and then fuse or cohere with the resin into a conducting ring. Carbon can also be used. As an alternative method, I prefer to use one of the well known low melting alloys that has a melting'` point from 60 to 150"l C. These low melting alloys are given in standard handbooks such as page 670 of the 1933 edition of Handthe Chemical Rubber Publishing Company of Cleveland, Ohio. The Vparticular alloys in this handbook have been designated as the bismuth alloys and one in particular that is especially suitable is an alloy o f 53% bismuth, 32% lead and 15% tin with a melting point of 96 C.

'I'he powdered natural resinand its plasticizer ls spread over the noble metal surface of the copper oxide ldisk and then the powdered low melting alloy is spre'ad around the 'desired contact area on the rim or edge of the natural-resin powder. heated to a temperature of about 135 C. The resin and plasticizer fuses to` aiL clear liquid in the central portion of the disk and the low melting alloy and the rosin fuse together to make a conductive contact carrier with the noble film.

An annular ring i6 of any suitable conductive metal such as tin or lead or zin'c and preferably tin plated steel makes contact with the conductive portion I5 of the preservative coating.

`.Any suitable typeof connectionrcan then be made to the annular ring i6 and to the copper base l without disturbing the sensitive portions of the cell. These connections Il and i8 may extend to a light meter I9 for example.

rlv'hevcell, as disclosed, is a ,self-generating cell of electricity in response to light acting upon the copper oxide and releasing electrons therefrom through the barrier plane to the noble metal film. The electrical connections from the,

negative electrode (the noble metal) through the low melting alloy r other metal to the annular ring I6 provide the negative terminalv of the cell and the copper on the other hand isl the positive terminal. The cell develops electricity at approximately %0 of a volt and the current depends upon the strength of the light energy received.4

It is to be'noted that the cell does not require an outside source 'of electricity.

Although I have shown and described certain specific embodiments of my invention, VI am fully aware that many modifications thereof are possible. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art.

I claim as my invention:

1. A photo-sensitive device comprising copper having a portion of its surface oxidized, a trans- The disk is then placed on a hot plate V lucent metallic coating upon said oxide, and a preservative and contact coating for said-metallic coating consisting of a layer of a natural resin with a conductive alloy at certain portions only, said alloy extending through said resin and having a melting point between 60 and'125 centigrade, said metallic coating and resin coating having suicient area clear of said alloy for the passage of light therethrough of the device.

2. A photo-sensitive device comprising a copper oxide layer having a translucent conductive film thereon, a natural resin layer fused on said for the actuation conductive film and a conductive material at a Y certain portion only in said natural resin making electrical contact through said natural resin to said conductive film, said conductive film and said natural resin layer4 having suflicient areav clear of said alloy for the passage of light therethrough for the actuation of `the device. i e

3. A photo-sensitive device comprising a copper oxide layer having a translucent conductive film thereon, a natural resin. layer on said conductive film and a conductive material fused at a certain portion only of said natural resin layer extending through said resin layer and makingv electrical contact with said translucent conductive film, said conductive film and Isaid natural resin layer -having sufcient area clear of said alloy for the passage of light therethrough for the actuation of the device.

4. A photo-sensitive device comprising a copper oxide disk havinga translucent conductive film thereon, a natural resin layer fused on said conductive film, and a conductive metal fused With the natural resin and extending through the thickness of said resin around the rim portion of said disk.

5. A photo-sensitive device comprising a copper oxide disk having a translucent conductive film thereon, a natural resin layer fused on said conductive lm, and a lconductive metal fused with the natural resin and extending through the thickness of said resin around the rim portion of said disk and a conductive ring superimposed on the conductive metal and natural resin.

6. The method of providing a coating for aphoto-sensitive device which comprises spreading over the surface that will receivethe light signal, powdered natural resin andV heating the resin until it fuses thereon.

7. The method of providing a coating for a photo-sensitive device which comprisesspreading over the surface, that will receive the light signal, powdered natural resin and plasticizer and applying heatuntil they fuse thereon.

l8. A photo-sensitive device comprising copper having a' portion of its surface oxidized, a. translucent metallic coating upon said oxide, and a preservative coating fused thereon consisting of a natural resin plasticized with a wax from the group consisting of paramn, Japan wax, normal butyl phthalate and ethylene.

9. A photo-sensitive device comprising copper having a portion of its surface oxidized, a translucent metallic coating upon' said oxide, and a preservative coating fusedthereon consistingof a natural resin selected from the group consistingof rosin, collophony, abietic acid, ester gum or glycerized rosin and plasticized with a waxv from the group .consisting of paraiiin, Japan wax, normal butyl phthalate and ethylene.

EARL D. W'rsoN. 

